Ultrasonic frequency generating crystal assembly



INVENTOR.

March 13, 1962 H. c. METTLER ULTRASONIC FREQUENCY GENERATING CRYSTALASSEMBLY Filed June 18, 1957 ENERGIZING CIRCUIT United States Patent3,025,419 ULTRASONIC FREQUENCY GENERATING CRYSTAL ASSEMBLY I-Ial C.Mcttler, 1709 Putney Road, Pasadena, Calif. Filed June 18, 1957, Ser.No. 666,344 Claims. (CI. 3109.1)

My invention relates to an ultrasonic frequency generating crystalassembly and included in the objects of my invention are:

First, to provide an ultrasonic frequency generating crystal assemblywherein all but the base surface of the crystal is exposed to the liquidinto which the ultrasonic energy is to be transmitted thereby not onlymaterially improving the efiiciency of transmission of the ultrasonicenergy but also materially improving the dissipation of heat generatedwithin the crystal.

Second, to provide an ultrasonic frequency generating crystal assemblywhich incorporates an effective but extremely simple and inexpensivemeans for electrical connection of the crystal as well as securing andsealing the crystal in its setting or mounting.

Third, to provide an ultrasonic frequency generating crystal assemblywhich is adapted to the utilization of relatively thin crystals forproducing the higher ultrasonic frequencies required in therapeuticapplications, and which in such applications, makes possible anextremely light weight and compact instrument capable of particularlyefficient transmission of ultrasonic frequencies to the patients body.

Fourth, to provide an ultrasonic frequency generating crystal which isalso adapted to the utilization of relatively large crystals forproducing the lower ultrasonic frequencies and having a substantialpower output such as required in ultrasonic cleaning procedures, andwhich in such applications, the maximum area of the crystal is exposedto heat exchanging contact with the transmitting liquid so that the heatgenerated in the crystal may be effectively dissipated, thus permittingmaximum power output from the crystal.

With the above and other objects in view as may appear hereinafter,reference is directed to the accompanying drawings, in which:

FIGURE 1 is a fragmentary side view of a therapeutic applicator with anultrasonic frequency transmitting crystal mounted therein in accordancewith my invention.

FIGURE 2 is a partial sectional, partial side view of the crystal asutilized for therapeutic purposes.

FIGURE 3 is an exaggerated fragmentary sectional view taken through 3-3of FIGURE 1 showing the manner in which the crystal is mounted in thetherapeutic applicator.

FIGURE 4 is a fragmentary perspective view of an ultrasonic frequencytransmitting crystal dimensioned for producing ultrasonic frequencies inthe lower range and shown mounted in a wall of a vessel intended tocontain the crystal and a cleansing liquid, the wall being shownfragmentarily.

FIGURE 5 is an end view of the crystal shown in FIG- URE 4 as it appearsbefore installation, with portions broken away and in section toillustrate the internal construction.

FIGURE 6 is an exaggerated fragmentary sectional view taken through 66of FIGURE 4 showing the manner in which the crystal is mounted in thewall of a container.

Crystals utilized for producing ultrasonic frequencies exhibitpiezoelectric properties and may be either natural or artificialcrystals or ceramics. One type of artificial crystal or ceramic which iswidely used is composed of barium titanate. This material has provedapplicable in 3,025,419 Patented Mar. 13, 1962 the exercise of myinvention; however, the invention is not limited to this material.

Reference is first directed to FIGURES l to 3 in which is illustratedthe application of my invention to a therapeutic instrument. In thisapplication, the crystal 1 is in the form of a relatively thin flatdisk. The thickness of the crystal determines the frequency of theultrasonic output of the crystal. The crystal is provided with a firstplating or coating 2 of conductive material on its bottom surface. Forexample, this may be a plating of silver. The conductive coating 2 ispreferably smaller in diameter than the crystal exposing an unplatedmargin 3.

A second conductive coating 4, which may also be a plating of silver, isapplied over the upper surface as well as its sides, and preferablyextends to the bottom surface. The conductive coatings are separated bythe unplated margin 3.

A protective coating 5 is applied over the upper surface of the crystaland is extended part way down the sides thereof to form a shoulder 5A.The protective coating is preferably a glaze such as used in coatingceramics and is baked on. A glaze is selected which can be bonded attemperatures which will not affect the underlying conductive coating 4.

The crystal thus prepared is adapted to be set in a mounting head 6which may be merely a cup-shaped spinning or stamping having a mouthdimensioned to receive the crystal. The periphery of the crystal belowthe protective coating 5 is coated with a conductive adhesive 7 such asan epoxy resin containing metal, commonly known as cold solder. Care istaken, of course, not to bridge the uncoated margin 3. The cold solderprovides an electrical connection between the conductive coating 4 andthe mounting head 6, affords a dependable mechanical connection to holdthe crystal in place, and also effectively seals the connection betweenthe crystal and the mounting head.

The crystal is connected, as indicated in FIGURE 1, to a suitableconventional energizing circuit by a ground lead connected to themounting head, and a second lead connected to the first conductivecoating 2. Application of electrical energy at the proper frequencycauses the crystal to expand and contract between its bottom and topsurfaces at a corresponding frequency and generate an ultrasonicfrequency predelivered by the thickness of the crystal.

The crystal is utilized by placing it in contact with the patients body.An oil or other liquid is applied to the crystal and to the patientsskin to provide a liquid transmitting medium. The oil or other liquidnot only serves to transmit the ultrasonic vibrations, but also tends todissipate heat from the crystal.

However, in the application of this invention to high frequencyultrasonic crystals for therapeutic purposes, the problem of heatdissipation, while present, is not the principal problem. It is,instead, the problem of efiicient transmission of the vibration from thecrystal to the body tissues. By reason of the fact that the crystal isin virtually direct contact with the skin or the transmitting liquid,that is, separated therefrom only by the metal plating or conductivecoating 4 and the protective coating 5, which need be only a fewthousands of an inch, the vibrations are transmitted with a minimum ofloss.

Reference is now directed to FIGURES 4 to 6. The construction hereillustrated is primarily directed to the use of crystals of substantialthickness and therefore intended to produce relatively low ultrasonicfrequencies. As noted previously, the operating frequency of the crystalis determined by its thickness. Thus, in the first instance hereinbeforedescribed, the crystal is in the order of an eighth of an inch inthickness and functions in the megacycle range, whereas, in theconstruction shown in FIGURES 4 to 6, the crystal may be in the range oftwo inches thick and operate in the range about twice that of audiblesound; for example, in the range of 40,000 cycles per second.

Crystals of the larger size have many uses, one of which is in effectingultrasonic cleaning of parts emersed in a liquid bath in which theliquid is caused by the crystal to vibrate at some selected ultrasonicfrequency. In such installations, the power output requirements of thecrystals is severe and heating problems are serious.

Thus, as shown in FIGURES 4 to 6, a relatively large, or thick, low,ultrasonic crystal 11 is utilized. The crystal is illustrated as arectangular block, the thickness of which, between its top side 12 andbottom side 13, determines its vibration frequency. For purposes ofoutput into the surrounding transmitting and cooling liquid, not shown,the crystal may be a cube, or have lateral dimensions greater than itsthickness; however, this would reduce the ability of the crystal todissipate its internal heat. Therefore, it is preferred to construct thecrystal with one lateral dimension as small as is consistent with goodoscillation characteristics.

The bottom or base side of the crystal is provided with a conductivecoating 14 which may, for example, be a plating of silver. The coatingpreferably terminates inwardly from the margins of the crystal asindicated by 15 to insulate the conductive coating. The top side 12 isprovided with a second conductive coating 16 which may be coextensivewith the top surface. The second coating 16 may extend part way down theside walls as in the case of the first described construction; however,in order to convert the crystal into a piezoelectric crystal, it isnecessary to impress the crystal with a direct current voltage manytimes greater than the operating voltage. In the case of relatively thincrystals as in the first described construction, this is not a problem,but in the case of crystals of substantial thickness, the impressingvoltage may be so high that conductive coating on the side walls cannotbe tolerated.

This also poses a problem of electrical connection with the secondcoating. This is solved by providing a small bore 17 through the crystalbetween the bottom and top sides which receives a conductor 18. Thebottom conductive coating 14 terminates clear of the bore 17 asindicated by 19. The upper end of the conductor is soldered or otherwiseelectrically connected, as indicated by 20, to the top or secondconductive coating 16. Installation of the conductor is made after theimpressing voltage has been applied to the crystal.

After installation of the conductor 18, the top and lateral sides arecoated with a glaze 21, or other protective coating, which seals thesurfaces of the crystal and provides insulation. As in the firstdescribed structure, any of the various glazes used on ceramics, havingthe requisite electrical properties and sufficiently low fusingtemperature as not to damage the conductive coating, may be used.

The protective coating preferably terminates short of the bottom side 13to form a shoulder 22 which aids in mounting the crystal. The crystal ismounted in a Wall 23, preferably the bottom wall of a vessel orcontainer which is intended to contain the cleaning solution and theparts to be cleaned. The bottom Wall 23 is provided with an aperturedimensioned to receive the crystal as shown in FIGURE 6. A coating of aresin adhesive, such as an epoxy adhesive 24, is applied around the baseof the crystal. In this case the adhesive need not be conductive. Theconductor 18 is grounded to the bottom wall 23 of the vessel so that thetop conductive coating, conductor, and vessel walls are maintained atground potential.

Except for the bottom side 13 and the narrow zone fitted within thebottom wall 23, the entire crystal is exposed to the liquid which fillsthe container or vessel in which the crystal is mounted. As aconsequence, heat may be radiated not only from the top side 12 but alsofrom all four lateral sides of the crystal directly into the liquid.This permits a corresponding increase in power which may be applied tothe crystal without the crystal overheating.

Although I have shown and described certain embodiments of my invention,I do not wish to be limited thereto, but desire to include in the scopeof my invention the novelty inherent in the appended claims.

I claim:

1. An ultrasonic frequency generating crystal assembly comprising agrounded conductive mounting member having an aperture therein, acrystal adapted, when energized, to generate an ultrasonic frequencypredetermined by its dimensions, the crystal having upper and lowerparallel surfaces and a side disposed between the surfaces, a firstconductive coating on at least a portion of the lower surface, a secondconductive coating covering at least a portion of the upper surface anda portion of the side of the crystal, the crystal being disposed withinthe aperture so that the upper surface of the crystal projects outwardlyfrom the mounting member, the mounting member being arranged to providea space adjacent substantially the entire lower surface of the crystal-to permit free movement of the lower surface of the crystal in adirection normal to the lower surface, a protective coating completelycovering at least the portion of the second conductive coating disposedon the upper surface, and conductive seal means disposed between aportion of the side extending completely around the crystal and themounting member to secure the side of the crystal to the mounting memberand to provide an electrical connection between the second coating andthe mounting member, the seal means being arranged to prevent electricalcontact between the first coating and the mounting member.

2. The combination as defined in claim 1 wherein the first coating isarranged toprovide an uncoated marginal area on the lower surfacecompletely surrounding the first coating to isolate the first coatingfrom the side of the crystal.

3. The combination as defined in claim 2 wherein the crystal iscylindrical, and wherein the second conductive coating is arranged tocompletely cover the upper surface of the crystal, the protectivecoating being arranged to completely cover the second conductive coatingdisposed on the upper surface of the crystal and a portion of theconductive coating disposed on the side of the crystal.

4. The combination as defined in claim 3 wherein the protective coatingdefines a shoulder completely surrounding the side of the crystal anddisposed between the upper and lower surfaces thereof.

5. In an ultrasonic frequency generating crystal assembly thecombination comprising a grounded conductive mounting member having acavity therein with an opening on one side of the member communicatingwith the cavity, a cylindrical crystal adapted, when energized, togenerate an ultrasonic frequency predetermined by its dimensions, thecrystal having upper and lower parallel surfaces and a peripheral sideextending between the surfaces, a first conductive coating on thecentral portion of the lower surface, the first conductive coating beingarranged to provide an uncoated marginal area on the lower surfacecompletely surrounding the first coating to isolate the first coatingfrom the side of the crystal, a second conductive coating completelycovering the upper surface and a portion of the side of the crystal, thecrystal being disposed within the cavity of the body member with theupper surface and a portion of the side of the crystal projectingoutwardly from the opening in the mounting member and the lower surfaceextending within the cavity to permit free undamped movement of thelower surface in a direction normal thereto, an epoxy resin having aconductive material embedded therein disposed between the mountingmember and at least the side portion of the crystal adjacent thereto forproviding a resilient mounting for the crystal and an electricalconnection between the second conductive coating and the mountingmember, and an insulating protective coating completely covering thesecond conductive coating disposed on the upper surface and the portionof the secand conductive coating disposed on the side of the crysmlwhich is not covered by the epoxy resin.

References Cited in the file of this patent UNITED STATES PATENTS2,283,285 Pohlman May 19, 1942 6 Erwin Nov. 18, Smoluchowski Jan. 25,Erwin Jan. 10, Fiske et a1. Feb. 26, Branson Ian. 19, Zapponi Apr. 9,Bradfield Aug. 20, Harris Feb. 24,

